204 TERRITORY AND REPRODUCTION 



the behaviour of animals without observing the 

 important part that habit plays in the life of the 

 individual ; an action performed to-day is liable 

 to be repeated to-morrow and the following day 

 until it becomes ingrained in the life of the 

 individual. This must not be taken to mean, 

 however, that a particular action has to be 

 performed for many days in succession before 

 it becomes definitely fixed ; if only it is repeated 

 a number of times, even within the space of 

 a few hours, it will acquire sufficient strength 

 for its continuance ; but continued repetition 

 gives increased fixity, and, as time goes by, it 

 becomes increasingly difficult for the creature to 

 make a change unless the character of the 

 situation necessitates readjustment. 



For example, when the organic condition 

 which leads to nest-building becomes active, 

 the bird tentatively collects some of the 

 necessary material in its bill, flies round with 

 it, and then drops it. After a while it collects 

 some more, and this time leaves it perhaps in 

 a bush. Later on it makes another attempt, 

 and, meeting with a situation which calls forth 

 the appropriate response, it thereupon lays the 

 foundation of the structure. We will assume 

 that the nest is placed in the midst of a tangled 

 bush. Well, the bird lays the first strands of 

 the foundation and then goes in search of more 

 material. The next time it approaches the nest 

 from the opposite side of the bush, and presently 

 it finds yet a third entrance. But each entrance 

 is not made use of in turn : one is employed 



